Frederick III (Danish: Frederik) was king of Denmark and Norway from 1648 until his death. He also governed under the name Frederick II as diocesan administrator (colloquially referred to as prince-bishop) of the Prince-Bishopric of Verden (1623–29 and again 1634–44), and the Prince-Archbishopric of Bremen (1635–45).

He instituted absolute monarchy in Denmark-Norway in 1660, confirmed by law in 1665 as the first in Western historiography. He also ordered the creation of the Throne Chair of Denmark. He was born the second-eldest son of Christian IV and Anne Catherine of Brandenburg. Frederick was only considered an heir to the throne after the death of his older brother Prince Christian in 1647.

In order to be elected king after the death of his father, Frederick conceded significant influence to the nobility. As king, he fought two wars against Sweden. He was defeated in the Dano-Swedish War of 1657–1658, but attained great popularity when he weathered the 1659 Assault on Copenhagen and won the Dano-Swedish War of 1658–1660. Later that year, Frederick used his popularity to disband the elective monarchy in favour of absolute monarchy, which lasted until 1848 in Denmark. He married Sophie Amalie of Brunswick-Lüneburg, with whom he fathered Christian V of Denmark.